The headlight (1) has a protective glass (3) formed of a rigid material transparent to light and mounted in front of a case (2) that is mounted on a body shell of a motor vehicle. The glass has a frangible weakening zone at a periphery part arranged between a front wall (3a) of the glass and the case. A non-deformable rigid part (5) integrated with the shell is arranged opposite to a rear part of the case which is supported on the part (5) during an impact applied on the glass in a manner to cause a rupture of the zone.
